1. Field of the Invention
This invention relates to a vehicle of the so called "off-road" type. More particularly, this invention relates to a hydrostatic system, such as may be employed in the off-road type vehicle in which over control compensation is provided to prevent burning out relief valves, pumps or wasting power.
2. Description of the Prior Art
A wide variety of off-road type vehicles have been known in the Prior Art. Each of the type vehicles have been expensive and have employed mechanical drives, electrical drives, and more recently, hydrostatic drives. As described in my co-pending application entitled "Adaptable Combination of Vehicle and Attachments", Ser. No. 919,179 (PF-331), filed June 26, 1978, and my co-pending application entitled "Off-Road Vehicle that both oscillates and articulates," Ser. No. 934,586, filed Aug. 17, 1978, there is provided an adaptable expensive vehicle that can be used with a wide variety of attachments such as augers, dump beds, ditch digging equipment, back hoes, revolving jib cranes, fork lifts and the like to more fully utilize the vehicle; and to provide a vehicle that is highly flexible, highly maneuverable, and able to be employed with such a wide variety of attachments. In the latter application, the vehicle was both oscillating and articulating so as to provide a level platform for operating attachments. The descriptive matter of these two applications are incorporated herein by reference for details omitted herefrom.
The prior art has seen the development of other attempts to provide overcontrol compensation in such an off-road vehicle. United States patents such as the following illustrate the state of the art technology. U.S. Pat. No. 2,161,439 shows a variable displacement pump and motor with an output control having a positive output lever operated by pressure acting against a spring. U.S. Pat. No. 2,262,563 shows a hydraulic system in which high pressure causes a shift of a lever toward neutral to lessen the output. This system also prevents reversal beyond a minor amount until pressure in the system falls below a damaging shock pressure. U.S. Pat. No. 2,976,685 shows a variable power transfer employing (1) a pressure operated ram to change the moment arm of displacement control with respect to fulcrum on the operators lever; (2) a caged spring between displacement control and lever and also indicates there is a coconnected fuel regulator to unload the transfer pump if excessive load is placed on the engine. U.S. Pat. No. 3,078,674 shows a hydraulic control system for a variable displacement pump in which pressure greater than a predetermined maximum effects centering of a pump control to reduce pump output. It uses diametrically opposed rams to center a wobble plate. U.S. Pat. No. 3,117,420 shows a hydrostatic transmission in which a follow up valve is positioned so that responsive to a control valve, double acting motion moves the displacement control to a maximum position and gradually reduces it as needed. In this apparatus the chamber pressure can load or unload to decrease or increase speed. U.S. Pat. No. 3,163,115 limits the volumetric rate of flow without objectionable feed back to the manual system. Cylinder 85 and piston 84 position the fulcrum responsive to volume and pressure from pump 20. It is a complex system to control rudders and the like. U.S. Pat. No. 3,327,475 shows a control system with a means for slowing the vehicle rather than stalling the engine if the torque requirements become too high. U.S. Pat. No. 3,660,975 shows a hydrostatic transmission with an automatic pump displacement control, manual override to keep the displacement low and the device sensitive to the pump inlet pressure to render the override inoperative when the pump inlet pressure exceeds a maximum. Spool 28 opens ports to increase or decrease pump capacity as needed.
These patents and applications represent a significant advance in the art but have not been totally satisfactory in solving all of the problems in the prior art.
In the prior art vehicles, there have been problems with the electric drives and with the mechanical drives that made a hydrostatic drive system advantageous. Yet the hydrostatic drive system was disadvantageous in that with the high flow capacity of its pumps for driving the vehicle, damage can be done if there was over pressuring such as when the vehicle encountered an immovable obstacle or the like. Even when relief valves were employed to relieve the pressure and prevent major structural damage, the relief valves could burn up in a very short time. Moreover, the relieving of the pressure wasted the power that could be advantageously used in a different way.
Moreover, the Prior Art vehicles needed foot controls in which the controls could only be operated in a given direction and could not be overridden, even if there was a strong operator, to prevent damage and wasting power.
Further, it was desirable that the off-road type vehicles that employed dual foot controls have foot controls in which the pedal not being employed was not uncomfortable to the operator.
Thus, it can be seen that the prior art was not totally satisfactory in providing an off-road vehicle that solved the deficiencies of the prior art in providing over control compensation, and allowing only one direction of pedal movement without discomfort to the operator in the opposite movement of the opposite and temporarily unused pedal.